Thick film compositions containing pyrochlore-related compounds

ABSTRACT

Film compositions are described which can be used as conductive, resistive or insulating films in a wide variety of electronic and light electrical components. Said films comprise a conductive phase based on pyrochlore-related compounds, and a dielectric phase based on glass.

FIELD OF THE INVENTION

[0001] This invention relates to film compositions which are applied tononconductive substrates to form conductive, resistive films in a widevariety of electronic and light electrical components. It particularlyrelates to such materials that contain pyrochlore-related compounds asthe conductive phase.

BACKGROUND OF THE INVENTION

[0002] Thick film materials are known in the art, which are mixtures ofmetal, glass and/or ceramic powders dispersed in an organic medium.These materials, which are applied to nonconductive substrates to formconductive, resistive or insulating films are used in a wide variety ofelectronic and light electrical components.

[0003] The properties of such thick film compositions depend on thespecific constituents of the compositions. Most of such thick filmcompositions contain three major components. A conductive phasedetermines the electrical properties and influences the mechanicalproperties of the final film. A binder, usually a glass and/orcrystalline oxide, holds the thick film together and bonds it to asubstrate and an organic medium (vehicle) acts as a dispersing mediumand influences the application characteristics of the composition andparticularly its rheology.

[0004] High stability and low process sensitivity are criticalrequirements for thick film resistors in microcircuit applications. Inparticular, it is necessary that resistivity (R_(av)) of a resistor bestable over a wide range of temperature conditions. Thus, thetemperature coefficient of resistance (TCR) is a critical variable inany thick film resistor. Because thick film resistor compositions arecomprised of a functional (conductive) phase and a permanent binderphase, the properties of the conductive and the binder phases and theirinteractions with each other and with the substrate affect bothresistivity and TCR.

[0005] Heretofore, thick film resistor compositions, and especially theair fired ones, have been formulated with cadmium and lead bearingglasses and Ru-based conducting materials. Some of the Ru-basedmaterials are RuO₂—see U.S. Pat. Nos. 3,868,334 and 4,101,708—or leadruthenate Pb₂Ru₂O_(6+δ)—see U.S. Pat. No. 3,682,840. A family ofpyrochlores such as Bi₂Ru₂O₇ and many other conducting oxides derivedfrom Bi₂Ru₂O₇ are described in U.S. Pat. Nos. 3,583,931 and 3,681,262.The use of these pyrochlores in thick film resistors is described inU.S. Pat. Nos. 3,560,410, 3,553,103 and 3,630,969. Lead and cadmiumcontaining glasses used in thick film resistors have been disclosed bynumerous U.S. Patents. U.S. Pat. No. 5,753,571 discloses lead andcadmium free glass compositions, containing specified amounts of bismuthoxide, silica and other oxides, for encapsulating electronic hybridcircuits. U.S. Pat. No. 5,439,852 discloses lead and cadmium free thickfilm compositions comprising electroconductive particles.

[0006] The air fired thick film resistors compositions of the prior arthave good properties. However, they have a number of shortcomings: e.g.,cadmium containing materials are known carcinogens and lead compoundsare highly toxic. Most producers of thick film resistors have addressedthe cadmium issue and have developed new Cd-free compositions.

[0007] Elimination of lead from thick film resistor composition is moredifficult and complex. The difficulty is probably due to the majorproportions of lead oxide in the conductive phase and in the glasses.Lead containing glasses have a unique combination of properties such asexpansion, viscosity, durability and surface tension, which make themvery desirable for thick film resistor compositions. Furthermore, whenconductive materials such RuO₂, Bi₂Ru₂O₇ and substituted bismuthruthenate are formulated with Cd- and Pb-free glasses, the resistancerange is too small for RuO₂ based resistors and the bismuthruthenate-type conductives interact with these glasses in such a waythat partial to complete leaching of Bi₂O₃ occurs. This interaction maybe described by: Bi₂Ru₂O₇+Cd- and Pb-free glass→RuO₂+Bi-glass. Theinteraction of bismuth ruthenate and substituted bismuth ruthenatecompounds with leadless glasses limits the resistance range and does notallow control of the resistance. The leaching of Bi₂O₃ from the bismuthruthenate-type conductive phases into the leadless glass may beprevented by the use of bismuthate glasses. However, bismuth ruthenateand substituted bismuth ruthenates, when formulated with bismuthateglasses, produce negative TCR. U.S. Pat. No. 5,491,118 describeslead-free and cadmium—free thick film resistor compositions. Said patentdescribes the use of Bi₂Ru₂O₇, BiGdRu₂O₇ and RuO₂ conducting phases withalkaline earth and bismuthate glasses. The bismuthate glasses aredescribed in the aforecited U.S. Pat. No. 5,439,852. Low resistanceresistors formulated with RuO₂ having good TCR are detailed and higherresistance resistors (˜30 kΩ) with BiGdRu₂O₇ are also detailed. However,at high resistance the TCR characteristics and especially the TCR gap,i.e., HTCR-CTCR are too large.

[0008] Thus, there is a need for new resistor compositions which are Cdand Pb-free and comprise a stable, air fired, conductive phase, whoseinteractions with the leadless glass are small. Moreover, the requiredresistance range should be in the range of ˜10 kΩ/□ to ˜mega Ω/□ withgood TCR characteristics (Ω/□ depicts surface resistance).

SUMMARY OF THE INVENTION

[0009] The invention provides film compositions that comprise, as aconductive phase, pyrochlore-related compounds of the general formulaM_(2-x) Cu_(x) Ru₂ O_(6+δ) wherein M is a rare earth metal selected fromthe rare earth metals of atomic number 60-71 inclusive, X=0.2-0.4, andδ=0-1.

[0010] By “pyrochlore-related compounds” are meant herein compounds thathave crystal structures close to that of pyrochlore. The structure ofall those compounds, as well as of pyrochlore, is identified bycharacteristic X-ray reflections. The structure of pyrochlore isdiscussed in U.S. Pat. No. 3,583,931, which lists various referencesdescribing it. The content of U.S. Pat. No. 3,583,931 and of thereferences cited therein is entirely incorporated herein by reference.

[0011] Some pyrochlore-related compounds of this invention are known andare described e.g. in A. Haouzi, J. Muller and L. C. Joubert,“Electrical and crystallographic characterization of pyrochlore phasesNd_(2-y) Cu_(y) Ru₂ O_(7-y)”, Mat. Res. Bull., 21, 1489-1493 (1986) and“Synthesis and sintering of mixed oxides with metallic conductivityNd_(2-x) Cu_(x) Ru₂ O_(7-x)”, J. Phys. Les. 47 (2), Cl-855-859 (1986),where their preparation is also taught. However, according to thisinvention, they are preferably prepared by a method which comprisesfiring in air, or at least in a non-reducing atmosphere, an admixture offinely divided particles of CuO, RuO₂ and a metal oxide selected fromthe rare earth metal oxides of atomic number 60-71 inclusive, at atemperature of at least 800° C.

[0012] The compositions of the invention also comprise a dielectricphase, which also acts as inorganic binder. Preferably, the dielectricphase consists of, or comprises as a main component, a glass phase. Morepreferably, according to the invention—the glass phase comprises a blendof two glasses. The first glass comprises by mole % 40-65% SiO₂, 1-15%B₂O₃, 12-27% BaO, 5-10% SrO, 5-15% CaO, 0-5% MgO, 0-5% Al₂O₃, 0-12%alkali metal oxides and 0-3% of a metal fluoride in which the metal isselected from the group consisting of alkali and alkaline earth metals.The second glass comprises glass forming compounds in a total amount of75 to 85 mole % wherein, said glass forming compounds comprise 40 to 65%SiO₂, 10 to 20% Bi₂O₃, 0.1 to 3% Al₂O₃, and glass modifiers in totalamount of 15 to 25%, wherein said glass modifiers comprise 1 to 23% ZnO,0.1 to 5% CuO, 0.1 to 5% CaO and 0.1 to 2% MgO, all of said percentagesbeing mole percentages. The term “glass-forming compounds”, as usedherein, includes the compounds each of which is capable of forming aglass by itself upon melting and cooling, such as SiO₂, as well as thecompounds which are usually known in the art as “conditionalglass-forming compounds”. Conditional glass-forming compounds, such asBi₂O₃, do not form a glass by themselves upon melting and cooling;however, they form a glass when mixed with another appropriate compound.Suitable glass-forming compounds, as defined above, may be, in additionto SiO₂, Bi₂O₃, and Al₂O₃, compounds selected, for example, from amongthe group consisting of B₂O₃, GeO₂, P₂O₅, Sb₂O₃, TeO₂, TiO₂ and ZrO₂ ormixtures thereof. Among these compounds, most preferred are B₂O₃, in anamount of at most 15 mole %, TiO₂ and/or ZrO₂, the sum of the amounts ofsaid TiO₂ and/or ZrO₂ being at most 5 mole % of the total glasscomposition. The total amount of all glass forming compounds, i.e.,SiO₂, Bi₂O₃, and Al₂O₃ and the optional additional glass formingcompounds, which are preferably selected from the group consisting ofB₂O₃, GeO₂, P₂O₅, Sb₂O₃, TeO₂, TiO₂ and ZrO₂ or mixtures thereof, is 75to 85 mole % of the total composition.

[0013] The term “glass modifiers” is herein used to define a class ofoxides and halogen compounds which do not possess the ability to form aglass by themselves upon melting and cooling, nor when combined withadditional compounds, other than, of course, compounds belonging to theclass of glasses forming compounds described above. However, the glassmodifiers are capable of modifying the chemical and physical propertiesof the glasses containing them. ZnO, CaO, CuO and MgO are known in theart as glass modifiers. Suitable glass modifiers which are optionallyincluded in the glass compositions according to the present invention,in addition to ZnO, CaO, CuO and MgO, may be selected, for example, fromthe group consisting of SrO, BaO, oxides and/or fluorides of alkalimetals, oxides of transition metals having an atomic number between 24to 28, inclusive, or mixtures thereof. The total amount of all glassmodifiers present in the glass composition—i.e., ZnO CaO, CuO and MgO,and the optional additional glass modifiers, which are preferablyselected from the group consisting of SrO, BaO, oxides and/or fluoridesof alkali metals, oxides of transition metals having an atomic numberbetween 24 to 28, inclusive, or mixtures thereof—is 15 to 25 mole % ofthe total composition.

[0014] The above definitions of the terms “glass-forming compounds” and“glass modifiers” are based on the general properties of the compoundsas they are known and accepted in the art.

[0015] The dielectric phase of the compositions of the invention mayinclude, in addition to or in place of glasses, other dielectrics, inparticular metal oxides, for example Al₂O₃, SiO₂, ZrSiO₄, ZrO₂ andaluminosilicates.

[0016] In order that the film compositions of the invention be adaptedto be applied onto a substrate, it is preferred that they shouldcomprise an organic vehicle. The organic vehicle does not criticallyaffect the electrical properties of the film compositions. Preferredtypes of such binders will be listed hereinafter.

[0017] Optionally, and in general preferably, the film compositions ofthe invention also include fillers, preferably chosen from the groupconsisting of Al₂O₃, SiO₂, ZrSiO₄, ZrO₂ and aluminosilicates.

[0018] In a preferred embodiment, the invention comprises screenprintable thick film paste compositions, suitable for thick filmresistor application, comprising

[0019] a) a dispersion of finely divided particles of thepyrochlore—related compound corresponding to the formula M_(2-x) Cu_(x)Ru₂ O_(6+δ) wherein M is a rare earth metal selected from the rare earthmetals of atomic number 60-71 inclusive, X=0.2-0.4 , δ=0-1;

[0020] b) the blend of glasses described hereinbefore, and;

[0021] c) dielectrics selected from SiO₂, ZrSiO₄, Al₂O₃, ZrO₂ andaluminosilicates.

[0022] More preferably, in the above chemical formula M is Neodymium Nd.

[0023] The invention further comprises a method of making filmcompositions by preparing a powdered mixture of a) 5-90% by weight of anoxide of the formula Cu_(x) M_(2-x) Ru₂ O_(6+δ) wherein M is a rareearth metal selected from the rare earth metals of atomic number 60-71inclusive, x is a number in the range of 0.25 to 0.4, and δ is a numberin the range of 0 to 1; and b) 95-10% by weight of dielectric materials.

[0024] Preferably, said method further comprises dispersing the powderedmixture in a liquid organic vehicle. Also preferably, the oxide ischosen from the group consisting of Nd_(1.70) Cu_(0.30) Ru₂ O_(6+δ),Nd_(1.75) Cu_(0.25) Ru₂ O_(6+δ), and their mixtures wherein δ is anumber in the range of 1 to 0; and the dielectric materials are chosenfrom the group consisting of glasses, oxides selected from ZrSiO₄,Al₂O₃, SiO₂, and mixture thereof.

[0025] The invention further comprises a method of preparingpyrochlore-related compounds, as hereinbefore defined, which comprisesfiring an admixture of finely divided particles of CuO, RuO₂ and a metaloxide selected from the rare earth metal oxides of atomic number 60-71inclusive, at a temperature of at least 800° C., in a non-reducingatmosphere. Particularly, said method is used for preparing compoundshaving the formula Nd_(2-x) Cu_(x) Ru₂ O_(6+δ), in which case itcomprises firing in air an admixture of finely divided particles ofNd₂O₃, CuO and RuO₂ at a temperature of 1000-1200° C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the drawings:

[0027]FIGS. 1 and 2 are X-ray diffraction diagrams of pyrochloresaccording to embodiments of the invention; and

[0028]FIG. 3 is a heating diagram used in sintering compositionsaccording to embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0029] A.—Pyrochlore-Related Compounds

[0030] The X-ray analysis shows that the compounds hereinbefore definedhave pyrochlore-related crystal structure. Hereinafter, they may bedesignated, for brevity's sake, by the sole term “pyrochlore”.

[0031] As has been said, they are preferably prepared by firing anadmixture of finely divided particles of CuO, RuO₂ and a metal oxideselected from the rare earth metal oxides of atomic number 60-71inclusive, at a temperature of at least 800° C. The compounds having theformula Nd_(2-x) Cu_(x) Ru₂ O_(6+δ) are preferably prepared by firing asadmixture of finely divided particles of Nd₂O₃, CuO and RuO₂ at atemperature of 800° C. to 1200° C., preferably of 1000-1200° C., in anon-reducing atmosphere, preferably in air.

[0032] The particle size of the pyrochlore components, i.e. Nd₂O₃, CuOand RuO₂, is not critical to the process of making the pyrochlore.However, it is preferred that they be finely divided to facilitatethorough mixing and complete reaction. A particle size of 0.1 to 80 μmis normally preferred. Some of the pyrochlore components such as Nd₂O₃and CuO may be introduced as nitrates Nd(NO₃)₃.xH₂O, Cu(NO₃)₂.xH₂O. Thecopper component maybe introduced as an organic salt or Cu₂O. Saidcomponents are typically at least 99 wt % pure and preferably have a99.5 wt % or even higher purity.

[0033] B. Inorganic Binder

[0034] Glass is most frequently used as inorganic binder for resistorscontaining the said pyrochlores and can be virtually any lead- andcadmium-free glass composition having a fiber softening point of below800° C. Preferred glass frits are used, such as the borosilicate frits,e.g. barium, calcium, other alkaline earth and alkali borosilicatefrits, in combination with bismuthate glass compositions, disclosed inU.S. patent application Ser. No. 09/143134, the contents of which isintroduced herein by reference. The preparation of the alkaline earthborosilicate glass frits is well known and consists, for example, inmelting together the constituents of the glass and pouring such moltencomposition into water to form the frit. The batch ingredients may, ofcourse, be any compound that will yield the desired oxides under theusual conditions of frit production. For example, boric oxide will beobtained from boric acid, silicon dioxide from flint, barium oxide frombarium carbonate; etc. The glass frit is preferably milled in a ballmill with water to reduce the particle size of the frit and to obtain afrit of substantially uniform size.

[0035] The preferred glass frits for use in the resistor compositions ofthe invention are those Cd- and Pb-free frits comprising a combinationof alkaline earth borosilicate frits with bismuthate frits disclosed inU.S. patent application Ser. No. 09/143134. The preferred alkaline earthborosilicate frits are those comprising, in mole percentages, 40-65%SiO₂, 1-15% B₂O₃, 12-27% BaO, 5-10% SrO, 5-15% CaO, 0-5% MgO, 0-5%Al₂O₃, 0-12% alkali metal oxides and 0-3% of a metal fluoride in whichthe metal is selected from the group consisting of alkali and alkalineearth metals.

[0036] The glasses are prepared by conventional glass-making techniques,by mixing the desired components in the desired proportions and heatingthe mixture to form a melt. As is well known in the art, heating isconducted to a peak temperature and for a time such that the meltbecomes entirely liquid and homogeneous. Preferably, in carrying out theinvention, the components are premixed by shaking in a polyethylene jarwith plastic balls and then are melted in a platinum crucible at thedesired temperature. The melt is heated at a peak temperature of 1100°C.-1400° C. for a period of 1-1.5 hours. The melt is then poured intocold water. The maximum temperature of the water during quenching iskept as low as possible by increasing the volume ratio of water to melt.The crude frit, after separation from water, is freed from residualwater by drying in air or by displacing the water by rinsing withmethanol. The crude frit is then ball milled for 3-15 hours in aluminacontainers using alumina balls. Alumina picked up by the frit, if any,is not within the observable limit, as measured by x-ray diffractionanalysis. After discharging the milled frit slurry from the mill, excesssolvent is removed by decantation and the frit powder is air-dried atroom temperature. The dried powder is then screened through a 325 meshscreen to remove any large particles.

[0037] The major two properties of the frit are that it aids the liquidphase sintering of the inorganic crystalline particulate materials andforms noncrystalline (amorphous) or crystalline materials bydevitrification during the heating-cooling cycle (firing cycle) in thepreparation of thick film resistors. This devitrification process canyield either a single crystalline phase having the same composition asthe precursor noncrystalline (glassy) material or multiple crystallinephases with different compositions from that of the precursor glassymaterial.

[0038] C. Organic Vehicle

[0039] The organic vehicle is usually a resin. The most frequently usedresin is ethyl cellulose. However, resins such as ethylhydroxy ethylcellulose, wood rosin, mixtures of ethyl cellulose and phenolic resins,polymethacrylates of lower alcohols, and monobutyl ether of ethyleneglycol monoacetate can also be used.

[0040] The most widely used solvents for dissolving the polymerscontained in the organic vehicle (which may contain other materials,such as surfactants, antioxidants, etc.) for thick film applications,are terpenes such as alpha- or beta -terpineol, or mixtures thereof withother solvents such as kerosene, dibutylphthalate, dibutyl carbitol,butyl carbitol acetate, hexylene glycol, and high boiling alcohols andalcohol esters. Various combinations of these and other solvents areformulated to obtain the desired viscosity and volatility requirementsfor each application.

[0041] Among the thixotropic agents, which may constitute the organicvehicle, which are commonly used are hydrogenated castor oil andderivatives thereof and ethyl cellulose. It is, of course, not alwaysnecessary to incorporate a thixotropic agent since the solvent/resinproperties coupled with the shear thinning inherent in any suspensionmay alone be suitable in this regard.

[0042] The ratio of organic medium to solids in the dispersions orsuspensions can vary considerably and depends upon the manner in whichthe dispersion is to be applied and the kind of organic medium used.Normally, to achieve good coverage the dispersions will contain 60-90 wt% of solids and 40-10 wt % of organic medium. Such dispersions areusually of semifluid consistency and are referred to commonly as“pastes”.

[0043] Pastes are conveniently prepared on a three-roll mill. Theviscosity of the pastes is typically within the following ranges whenmeasured at room temperature on Brookfield viscometers at low, moderateand high shear rates: Shear Rate (sec⁻¹) Viscosity (Pa · s) 0.2 100-5000 —  300-2000 Preferred  600-1500 Most preferred 4  40-400 —100-250 Preferred 140-200 Most preferred 384  7-40 — 10-25 Preferred12-18 Most preferred

[0044] The amount and type of organic vehicle used is determined mainlyby the final desired formulation viscosity and print thickness.

[0045] D—Formulation and Application of the Compositions

[0046] In the preparation of the compositions of the present invention,the particulate inorganic solids are mixed with the organic vehicle anddispersed with suitable equipment, such as a three-roll mill or amuller, to form a suspension, resulting in a composition for which theviscosity will be in range of about 100-150 Pa.s at a shear rate of 4sec⁻¹. In the examples which follow, the composition is prepared in thefollowing manner: The ingredients of the paste, minus about 5 wt % ofthe estimated organic components which will be required, are weighedtogether in a container. The components are then vigorously mixed toform a uniform blend; then the blend is passed through dispersingequipment such as a three-roll mill to achieve a good dispersion ofparticles. A Hegman gauge is used to determine the state of dispersionof the particles in the paste. This instrument consists of a channel ina block of steel that is 25 μm deep (1 mil) at one end and ramps up tothe metal surface—0″ depth—at the other end. A blade is used to drawdown paste along the length of the channel. Scratches will appear in thechannel where the agglomerates diameter is greater than the channeldepth. A satisfactory dispersion will give a fourth scratch point of10-8 μm typically. The point at which half of the channel is uncoveredwith a well dispersed paste is between 3 and 8 μm typically. The numberof continuous scratches is counted. If the fourth scratch starts at 20μm and the channel is covered by paste at 10 μm, this indicates a poorlydispersed suspension.

[0047] The remaining 5% of the organic components of the paste is thenadded and the resin content of the paste is adjusted to bring theviscosity when fully formulated to between 140 and 200 Pa.s at a shearrate of 4 sec⁻¹.

[0048] The composition is then applied to a substrate such as aluminaceramic, usually by the process of screen printing, to wet thickness ofabout 30-80 microns, preferably 35-70 microns and most preferably 40-50microns. The resistor compositions of this invention can be printed ontothe substrates either by using an automatic printer or a hand printer inthe conventional manner. Preferably automatic screen stencil techniquesare employed using 200 to 325 mesh screen. The printed pattern is thendried at below 200° C., e.g., about 150° C., for about 5-15 minutesbefore firing. Firing to effect sintering of both the inorganic binderand the finely divided particles of conductive phase is preferably donein a well ventilated belt conveyor furnace with a temperature profilethat will allow burnout of the organic matter at about 300°-600° C., aperiod of maximum temperature of about 800°-950° C. lasting about 5-15minutes, followed by a controlled cooldown cycle to preventoversintering, unwanted chemical reactions at intermediate temperaturesor substrate fracture which can occur from too rapid cooldown. Theoverall firing procedure will preferably extend over a period of about 1hour, with 20-25 minutes to reach the firing temperature, about 10minutes at the firing temperature and about 20-25 minutes in cooldown.In some instances, total cycle times as short as 30 minutes can be used.

[0049] E—Sample Preparation

[0050] a) Thick Film Resistors

[0051] Samples to be tested for temperature coefficient of resistance(TCR) are prepared as follows:

[0052] A pattern of the resistor formulation to be tested is screenprinted upon each of ten coded Alsimag 614 1×1″ ceramic substrates andallowed to equilibrate at room temperature and then dried at 150° C. Themean thickness of each set of ten dried films before firing must be22-28 microns as measured by a light section microscope. The dried andprinted substrate is then fired for about 60 minutes using a cycle ofheating at 35° C. per minute to 850° C., dwell at 850° C. for 9 to 10minutes and cooled at a rate of 30° C. per minute to ambienttemperature.

[0053] b) Pellets

[0054] The ingredients which consist of glasses, conductive phase anddielectric were ground together in an agate mortar using analyticalethanol to ensure proper mixing. A few drops of polyvinyl alcoholsolution in water were added to the dry mixed powder to increase thegreen strength of the pellets. Pellets were prepared by pressing ˜0.2 gof mixed ingredients in a Carver press; typically, 4000 lbs on a pelletdie of 6 mm diameter result in a pressure of ˜5000 kg/cm². The pelletswere sintered by placing them on platinum foil and heating them in a boxfurnace using the temperature profile of FIG. 3.

[0055] After sintering, the pellets dimensions (diameter and thickness)were recorded and one face of the pellet was coated with silver paste(DuPont 6160 Ag conductor composition).

[0056] After drying the silver paste, the pellets were placed on a 96%alumina substrate and were heated to 850° C. using the sintering profileof FIG. 3. After the second heating, the second face of each pellet wascoated with Ag paste, dried and subjected to the same heating profile ofFIG. 3. The above detailed procedure of pellet preparation requiredthree heatings at peak firing of 850° C. (FIG. 3), and is referred to asprocess I. A second firing procedure was the cofiring of the greenpellets with the dried silver paste on both faces of the pellet, and isreferred to as process II. Process II uses the heating profile of FIG.3, and the substrate on which the pellets are placed is 96% alumina.

[0057] After sintering and coating with silver paste, the electricalresistances of the pellets were measured (two probes technique) at roomtemperature and 125° C. Resistivity and temperature coefficient ofresistance (TCR) were estimated from the measured resistance and pelletdimensions. Temperature coefficient of resistance for the range of 25°C. to 125° C. is referred to as hot TCR or HTCR and for −55° C. to 25°C. range as cold TCR or CTCR.

[0058] F—Resistance Measurement and Calculations

[0059] Substrates prepared as described above are mounted on terminalposts within a controlled temperature chamber and electrically connectedto a digital ohmmeter. The temperature in the chamber is adjusted to 25°C. and allowed to equilibrate, after which the resistance of eachsubstrate is measured and recorded. The temperature of the chamber isthen raised to 125° C. and allowed to equilibrate, after which theresistance of the substrate is again measured and recorded. Thetemperature of the chamber is then cooled to −55° C. and allowed toequilibrate and the cold resistance is measured and recorded.

[0060] The temperature of the chamber is then cooled to −55° C. andallowed to equilibrate and the cold resistance measured and recorded.The hot and cold temperature coefficients of resistance (TCR) arecalculated as follows: $\begin{matrix}{{{Hot}\quad {TCR}} = {\frac{R_{125^{\circ}\quad {C.}} - R_{25^{\circ}\quad {C.}}}{R_{25^{\circ}\quad {C.}}} \times \left( {10,000} \right)\quad {{ppm}/{{\,^{\circ \quad}C}.}}}} \\{{{Cold}\quad {TCR}} = {\frac{R_{{- 55^{\circ}}\quad {C.}} - R_{25^{\circ}\quad {C.}}}{R_{25^{\circ}\quad {C.}}} \times \left( {{- 12},500} \right)\quad {{ppm}/{{\,^{\circ}\quad C}.}}}}\end{matrix}$

[0061] The values of R_(25° C.) and Hot and Cold TCR are averaged andR_(25° C.) values are normalized to 25 microns dry printed thickness andresistivity is reported as ohms per square at 25 microns dry printthickness. Normalization of the multiple test values is calculated withthe following relationship:

Normalized Resistance=R _(mes) .d _(mes)/25 μm

[0062] where R_(mes) is the average measured resistance and d_(mes) isthe average measured thickness

[0063] Some samples were measured manually by two probes technique atroom temperature, 125° C. and −55° C., hot and cold TCR were estimatedusing the equations given above.

[0064] G—Coefficient of Variance

[0065] The coefficient of variance (CV) is a function of the average andindividual resistances for resistors tested and is represented by therelationship σ/R_(av), wherein$\sigma = \sqrt{\frac{\sum_{i}\left( {R_{i} - R_{a\quad v}} \right)^{2}}{n - 1}}$

[0066] R_(i)=Measured resistance of individual sample.

[0067] R_(av)=calculated average resistance of all samples(Σ_(i)R_(i)/n)

[0068] n=number of samples

[0069] CV=σ/R_(av)X100

EXAMPLES 1 AND 2

[0070] The compounds Nd_(1.75) Cu_(0.25) Ru₂ O_(6+δ) and Nd_(1.7)Cu_(0.3) Ru₂ O_(6+δ), briefly referred to hereinafter as “Example 1” and“Example 2” respectively, were synthesized by solid state reaction ofthe appropriate amounts of CuO, Nd₂O₃ and RuO₂. The well ground mixturesof the oxides in the appropriate proportions were placed in platinumcrucibles and heated in an electric furnace in air at 1100-1200° C.

[0071] Example 1 was heated at 1100° C. for 40 to 60 hrs withintermittent grindings. Example 2 was subjected to the same thermaltreatment as Example 1 and further heated 8 hrs at 1200° C. Example 1was vibratory milled in a Sweco vibratory mill to provide finely dividedpowder. Example 2 was used as such with no grindings.

[0072] X-ray diffraction of the resulting black powders are given inFIGS. 1 and 2 for Examples 1 and 2 respectively. The x-ray diffractionanalysis shows that these compounds are pyrocholore-type.

[0073] Papers published by A. Haouzi, J. Muller and L. C. Joubert,“Electrical and crystallographic characterization of pyrochlore phasesNd_(2-y) Cu_(y) Ru₂ O_(7-y)”, Mat. Res. Bull., 21, 1489-1493 (1986) and“Synthesis and sintering of mixed oxides with metallic conductivityNd_(2-x) Cu_(x) Ru₂ O_(7-x)”, J. Phys. Les. 47 (2), Cl-855-859 (1986),contain data on the synthesis and properties of these pyrochlores.

EXAMPLES 3-10

[0074] The glasses were prepared by the above method, milled andcharacterized by Differential Thermal Analysis (DTA) and dilatometer.The glass transition temperature (Tg) as obtained from DTA anddilatometric measurements were in the range of 300°-550° C.

[0075] Glasses in accordance with the invention are given in Table I.

[0076] Compositions in mole % are given in Table I for the experimentalglasses (examples 3-8) and in wt % for two commercial lead containingglass frits made by-Hammond Lead Products Inc., Hammond, Ind. USA. Thecommercial glass frits were vibratory milled. TABLE I Glass compositionsin mole % (ex.3-8) and in wt % (ex 9-10) Example No. 3 4 5 6 7 8 9 10BaO 27.0 22.20 15.0 — — — — — SrO 8.0 7.11 5.0 — — — — — CaO 5.0 4.4412.0 4.00 4.27 2.00 — — MgO 5.0 — — 1.00 2.45 1.0 — — CuO — — — 3.003.10 2.0 — — ZnO — — — 17.00 13.67 10.0 — — Bi₂O₃ — — — 17.00 17.89 20.0— — K₂O — 6.22 3.0 — — — — — PbO — — — — — 65.0 65.0 Al₂O₃ — — — 2.003.31 2.0 1.00 3.00 B₂O₃ 5.00 5.00 10.0 — — — — — SiO₂ 50.0 55.00 55.056.0 55.31 63.0 34.0 32.0

EXAMPLES 11-17

[0077] Pellets Study

[0078] The ingredients which consist of glasses, conductive phase anddielectric were ground together in an agate mortar using analyticalethanol to ensure proper mixing. A few drops of polyvinyl alcoholsolution in water were added to the dry mixed powder to increase thegreen strength of the pellets. Pellets were prepared by pressing ˜0.2 gof mixed ingredients in a Carver press; typically, 4000 lbs on a pelletdie of 6 mm diameter were used, a pressure of ˜5000 Kg/cm². Most of thepellets were sintered by placing them on platinum foil and heating themin a box furnace using the temperature profile of FIG. 3.

[0079] After sintering, the pellets' dimensions (diameter and thickness)were recorded and one face of the pellet was coated by silver paste(DuPont 6160).

[0080] After drying the silver paste, the pellets were placed on a 96%alumina substrate and were heated to 850° C. using the sintering profileof FIG. 3. After the second heating, the second face of each pellet wascoated with silver paste, dried and subjected to the same heatingprofile of FIG. 3. The above detailed procedure of pellet preparationrequired three heatings at peak firing of 850° C. (FIG. 3), and isreferred to as process I. A second firing procedure was the cofiring ofthe green pellets with the dried silver paste on both faces of thepellet, and is referred to as process II. Process II profile made use ofthe temperature profile of FIG. 3 and the substrate on which the pelletswere placed was 96% alumina.

[0081] After sintering and Ag coating, the electrical resistances of thepellets were measured (two probes technique) at room temperature and125° C. Resistivity and temperature coefficient of resistance (TCR) wereestimated from the measured resistance and pellet dimensions.Temperature coefficient of resistance for the range of 25° C. to 125° C.is referred to as hot TCR or HTCR and for −55° C. to 25° C. range ascold TCR or CTCR.

[0082] Pellets compositions in wt % are given in Table II. Typically 4-6pellets were prepared for each composition. The pellets are identifiedby numbers added to the composition code; for example pellets number 3and 5 of Example 15 composition are coded 15-3 and 15-5 respectively.Pellets resistances, dimensions after sintering, estimated resistivitiesand the type of processing schedule are collected in Table III.

[0083] Compositions of Examples 11, 12 and 13 illustrate the effect ofincreasing filler (zircon) concentration for constant conductive phaseconcentration and fixed ratio of the glasses. Table III shows that theresistivity increases in the order of ρ₁₁>ρ₁₂>ρ₁₃ and the TCR increasesmonotonically with the filler concentration.

[0084] The compositions of Examples 14 to 17 were formulated with oneglass which is harder than the glass of Example 6, which is bismuthateglass. Conductive phase concentration was kept at fairly low level toassess the high resistance range of these compositions. Table III showsthat the glass of Example 4 imparts larger TCR than the mixed glassessystem (Examples 11, 12 and 13) and the resistivity is very high at 10wt % conductive phase concentration. At fixed conductive phaseconcentration of 15 wt % and increasing filler concentration, samples15, 16 and 17 show that the resistivity decreases with the increase inthe filler concentration and the TCR increases monotonically. TABLE IIPellets composition in wt % Example No. Ingredients 11 12 13 14 15 16 17Ex. 4 glass 22.5 21.25 20.0 80.0 75.0 70.0 65.0 Ex. 6 glass 22.5 21.2520.0 — — — — Ex 2. 50.0 50.0 50.0 10.0 15.0 15.0 15.0 Conductive phaseZr SiO₄ 5.0 7.50 10.0 10.0 10.0 15.0 20.0

[0085] TABLE III Resistances (Ω), resistivities (Ω cm), dimensions andprocessing procedure of pellets. Resistivity Example DimensionsResistance (Ω) (Ω cm) Processing No. D (mm) H (mm) RT 125° C. RT TCR(ppm/° C.) Procedure 11-1 5.54 1.86 0.870 0.920 1.13 574.7 Process I11-2 5.75 2.85 1.066 1.120 0.97 506.6 ” 11-3 5.41 1.71 0.946 0.994 1.28507.4 ” 12-1 5.61 1.98 0.903 0.957 1.13 598.0 ” 12-2 5.64 1.37 0.6770.217 1.24 590.8 ” 12-3 5.55 1.31 0.641 0.682 1.19 639.6 ” 13-1 5.621.14 0.421 0.451 0.92 712.6 ” 13-2 5.73 1.15 0.385 0.416 0.86 805.2 ”13-3 5.69 1.02 0.340 0.369 0.85 852.9 ” 14-1 5.47 2.11 23405 26960 260191518.9 ” 14-2 5.60 2.19 16512 19410 18575 1755.1 ” 14-3 5.41 2.32 6107069710 60573 1414.8 ” 15-1 5.55 2.03 212 275 252.9 2971.7 ” 15-2 5.712.64 252 325 244.6 2896.8 ” 15-3 5.65 2.98 329 421 416.1 2796.4 ” 16-15.79 1.92 2.86 3.48 2.94 2167.8 ” 16-2 5.71 1.58 3.02 3.61 4.91 1953.6 ”16-3 5.80 1.64 2.92 3.51 4.70 2020.5 ” 17-1 5.67 1.07 865 1076 2044.32439.3 ” 17-2 5.69 1.13 1245 1511 2808.0 2136.5 ” 17-3 5.65 1.04 20592529 4956.7 2282.7 ” 14-4 * Process II 14-5 * ” 15-4 * ” 15-5 * ” 16-4 *” 16-5 * ” 17-4 303.1 ” 17-5 337.0 ”

[0086] Thick film pastes were prepared on a three roll mill or Hoovermuller. The preparation using the three roll mill was described aboveand the procedure for the muller was: ˜10 g batch was prepared by mixing7 g solids with 3 g of organic materials. Mixing was done on the muller;which produces an action of shearing the paste ingredients between twoglass disks, where one of them is stationary and the second is rotating.Organic materials used were solutions of ethyl cellulose in solventssuch as terpineol and dibutylcarbitol. Pastes were screen printed (AMIscreen printer model 465) onto 1″×1″ 96% alumina substrates. Prior toresistor paste printing the alumina substrates were metallized withsilver paste, DuPont 6160. All pastes processing, after drying stage of20 minutes at 125° C., were done in a belt furnace (BTU, 4 zone) usingstandard 850° C. profile.

[0087] Electrical properties were measured by two probes technique usingKeithly 197 and Fluke meters. Standard techniques were used to measureresistances at 125° C. and minus 55° C. for HTCR and CTCR estimations.Two pastes were prepared on the muller using Ex. 1 conductive phase, Ex.7 glass and zircon. These pastes and 1:1 blend between them constituteExamples 18, 19 and 20. Compositions and electrical properties of theseExamples are given in Table IV. TABLE IV Composition in wt % andelectrical properties Example No. 18 19 20 Ex. 1 20.0 30.0 40.0Conductive phase Ex. 7 Glass 45.0 35.0 25.0 Zr SiO₄ 5.0 5.0 5.0 organics30.0 30.0 30.0 R (Ω/□/20μ)* 6.1576 × 10⁶ 427.2 128.8 CV (%) 74.7 2.562.26 HTCR (ppm/° C.) −953.4 151.0 157.3 σ_(HTCR) (ppm/° C.) ±328.0 ±8.8±10.2 CTCR (ppm/° C.) −1385.0 184.1 269.1 σ_(CTCR) (ppm/° C.) ±939.0±8.4 ±3.5

[0088] Table IV shows that the Ex. 1 conductive phase behaves in asimilar fashion to conductive phases used in current thick filmresistors. At 40 wt % conductive phase (ex. 20), the TCR is positive andsmall for both the HTCR as well as the CTCR. The resistance spread isvery tight as judged by the small coefficient of variance. At 30 wt %conductive phase (ex. 19) the resistance is higher, TCR small andpositive and the coefficient of variance is small. At 20 wt % conductivephase (ex. 18) the resistance is very high and TCR decreased and becamenegative. Negative TCR is expected since ex. 7 glass is a bismuthateglass and bismuthate glasses are known to impart negative TCR. Thezircon filler was added to raise the composite viscosity during firing.However, as will become evident from the following examples, it alsoacts to raise the TCR in these compositions.

EXAMPLES 21-29

[0089] Compositions and properties are given in Table V. Examples 21 to25 illustrate the electrical properties of system based on Ex. 1conductive phase with Ex. 6 glass without zircon. Examples 26 to 29illustrate the electrical properties of a system based on Ex. 1conductive phase, Ex. 8 glass and zircon. It is clear that Examples 26to 29, formulated with zircon, have higher (more positive) TCR thanExamples 21 to 25 which were formulated without zircon. These examplesalso illustrate the resistance range. TABLE V Composition in wt % andelectrical properties Example No. 21 22 23 24 25 26 27 28 29 Ex. 1Conductive 20.0 40.0 30.0 17.50 15.0 40 30.0 20.0 15.0 phase Ex. 6 Glass50.0 30.0 40.0 52.50 55.0 — — — — Ex. 8 Glass — — — — — 25 35.0 45.050.0 Zircon — — — — — 5.0 5.0 5.0 5.0 Organics 30.0 30.0 30.0 30.0 30.030.0 30.0 30.0 30.0 R (KΩ/□) 55 0.377 16.7 144 288 0.0893 0.93 4.6 18.2CV (%) 7 11.7 7.7 16.0 14 6.08 8.28 11.9 8.55 Fired 14 9.2 12.7 9.1 1015.0 13.0 13.5 12.8 thickness (μ) HTCR −748 −194 −722 −834 −887 150.6−100.8 −200.3 −286.3 (ppm/° C.) σ_(HTCR) (ppm/° C.) CTCR(ppm/° C.)−1387.6 −419 −1369.5 −1667.4 −1769.4 168.0 −248.3 −434.1 −565.5 σ_(CTCR)(ppm/° C.)

EXAMPLES 30-34

[0090] Table VI illustrates the electrical properties of Ex. 1conductive phase with examples 9 and 10 glasses. These commerciallyavailable lead glasses are typical of glasses used in current thick filmresistor compositions. Table VI shows that Ex. 1 conductive phasebehaves like lead ruthenate with leaded glass (Examples 30, 32 and 34).Composition of Examples 30 and 31 shows that the Ex. 10 glass, whichcontains more Al₂O₃, results in an increase in resistance, about oneorder of magnitude, at the same loading of conductive phase. TCR ispositive and the TCR gap (HTCR-CTCR) is small. In addition, the TCR ispositive and small at high resistance, a very desirable property. TABLEVI Compositions in wt % and electrical properties Example No. 30 31 3233 34 Ex. 1 Cond. 20.0 20.0 15.0 20.0 40.0 phase Ex. 9 glass 50.0 — 55.045.0 30.0 Ex. 10 glass — 50.0 — — — Zr SiO₄ — — — 5.0 — Organics 30.030.0 30.0 30.0 30.0 R(Ω/□) 73175 837173 3636200 97110 179.9 CV (%) 4.089.31 26.42 9.54 HTCR (ppm/° C.) 257.6 −13.4 206.2 585.6 σ_(HTCR) (ppm/°C.) ±6.0 ±9.6 ±8.5 ±16.1 CTCR (ppm/° C.) 237.3 −102.7 −87.0 147.6 792.4σ_(CTCR) (ppm/° C.) ±6.6 ±9.7 ±88.0 ±13.1 ±17.4

EXAMPLES 35-37

[0091] Table VII illustrate the effect of mixed glasses on electricalproperties. Examples 35 to 37 were formulated with fixed concentrationof Ex. 1 conductive phase (30 wt %) and varying ratio of Ex. 8 glass toEx. 3 glass. Table VI shows that as the ratio Ex. 3 glass/Ex. 8 glassincreases the resistance increases and the TCR decreases. This behaviorcan be utilized to adjust resistance, TCR and to obtain lower noise andbetter voltage performance; noise and better voltage performance improvewith the increase in the conductive phase concentration. TABLE VIICompositions in wt % and electrical properties Example No. 35 36 37 Ex.1 Conduct.phase 30.0 30.0 30.0 Ex. 8 Glass 30.0 20.0 10.0 Ex. 3 Glass10.0 20.0 30.0 Organics 30.0 30.0 30.0 R (KΩ/□) 0.45 1.53 7.5 CV (%) 4.55.8 8 Fired 15.7 12.6 12.0 thickness (μ) HTCR (ppm/° C.) 73.4 −81.9−266.6 σ_(HTCR) (ppm/° C.) CTCR (ppm/° C.) 11.7 −224.3 −536.8 σ_(CTCR)(ppm/° C.)

[0092] Pellets similar to Example 17 were prepared with Example 1conductive phase, Example 4 and Example 5 glasses and zircon.Compositions are given in Table VIII and properties in Table IX. Fivepellets were prepared for each composition and are identified by thenumbers following the example numbers, i.e., pellet #4 of Example 38 is38-4. Pellets 1 to 3 were processed by process I and pellets 4 and 5 byprocess II (cofiring). Table IX shows that Example 1 conductive producesvery low resistance with Example 4 glass in process I, and higherresistance in process II. The TCR is high and positive. With Example 5glass, which has a lower softening point than Example 4 glass, thepellets 39-1, 39-2 and 39-3 (process I) deformed to preclude meaningfulcomparison. Pellets 4 and 5, i.e., 39-4 and 39-5 made by process II, hadhigher resistance and lower TCR; one pellet 39-4 had negative TCR and39-5 with lower resistance (134 Ω) had positive TCR. According to TableIII, the estimated resistivities are slightly larger than the measuredresistance at room temperature, therefore, we may assume that theresistivities of 39-4 and 39-5 are about 700 and 150 Ω.cm respectively.Translation of these resistivities to thick film resistors via:$R = {\rho \frac{1}{w \cdot d}}$

[0093] wherein R is resistance in Ω, ρ resistivity in Ω. cm, 1 length incm, w width in cm, and d thickness in cm; and assuming one square, i.e.,1=w, then R=ρ/d and for typical thick film resistor d˜10μ=10⁻³ cm, oneobtains that resistivities of 700 and 150Ω cm translate to 700 000Ω/ and150 000Ω/ thick film resistances. TABLE VIII Pellets composition in wt %Example No. Ingredients 38 39 Example 4 glass 65.0 — Example 5 glass —65.0 Example 1 15.0 15.0 conductive Zr SiO₄ 20.0 20.0

[0094] TABLE IX Resistances (Ω), resistivities (Ω cm) dimensions andprocessing procedure of pellets. Resistance Dimensions (Ω) Example D(mm) RT Resistivity TCR Processing No. H (mm) 125° C. (Ω cm) (ppm/° C.)Procedure 38-1 5.72 1.59 0.75 0.86 1.21 1396 Process I 38-2 5.70 1.560.71 0.81 1.16 1341 ” 38-3 5.73 1.52 0.73 0.84 1.24 1435 ” 38-4 — — 18.019.30 — 687.8 Process II 38-5 — — 5.06 5.51 — 846.9 ” 39-1 — — * — — —Process I 39-2 — — * — — — ” 39-3 — — * — — — ” 39-4 — — 689 679 —−138.2 Process II 39-5 — — 134 138.7 — 334.0 ”

EXAMPLES 40-46

[0095] The theoretical relationship between the pellet's resistivity andthe expected resistance in thick film resistor, i.e., R=p/d wherein R isthe thick film resistance in Ω/ , d is the fired film thickness and p isthe pellet resistivity, was applied to Examples 38 and 39: pastecompositions based on Example 39 and blend of 38 and 39 andmodifications of these pastes were prepared. Their compositions andelectrical properties are given in Table X. The theoretical relationshipmentioned above is expected to apply if the pastes do not interact withthe substrate and the terminations. It is well known that lead-basedthick film compositions interact with the substrate and the terminationsstrongly. These leadless thick film compositions, examples 40 and 41,had very high resistances: R>240 MΩ/ for the 1×1 mm² resistors. Examples42 and 43 are modifications of examples 40 and 41, in which theconductive phase concentration was increased. Table X shows thatexamples 42 and 43 have resistances in the useful ranges with positiveHTCR (Example 43) and negative HTCR (Example 42).

[0096] Example 44 is 1:1 blend between examples 42 and 43, and Example45 is a ⅔:⅓ blend between Example 43 and Example 41, respectively.Example 46 is 1:1 blend between Example 41 and Example 43.

[0097] Example 46 was made on three roll mill and represents amodification of Example 45. The electrical properties show resistance inthe range of 10 kΩ/ to 100 kΩ/ with positive TCR. TABLE X Compositionsin wt % and electrical properties Ex. No. 40 41 42 44 44 45 46 ex. 110.50 10.50 31.50 31.50 31.50 24.50 20.00 conductive ex. 5 36.40 45.5025.20 31.50 28.35 36.17 39.50 glass ex. 6 9.10 — 6.30 — 3.15 — — glassZrSiO₄ 14.00 14.00 7.00 7.00 7.00 9.33 10.50 Organic 30.00 30.00 30.0030.00 30.00 30.00 30.00 Vehicle R (KΩ/) * * 17.866 0.669 29.88 4.04918.85 CV (%) 5.60 7.19 26.51 10.93 8.00 HTCR −347.3 462.6 −490.5 220.6170.2 (ppm/° C.) σ_(HTCR)(ppm/ ±41.2 ±33.6 ±56.5 ±40.5 ±31.5 ° C.) CTCR— — — 61.8 (ppm/° C.) σ_(CTCR)(ppm/ — — — — ±42.0 ° C.) Dry — — — — —thickness (μ)

EXAMPLES 47-49

[0098] TABLE XI Compositions in mole % and glass properties* Example No.47 48 49 SiO₂ 55.0 55.0 50.0 B₂O₃ 10.0 10.0 15.0 BaO 12.0 3.24 3.24 SrO5.0 3.24 3.24 CaO 10.0 3.24 3.24 CuO — 2.16 2.16 ZnO — 15.12 15.12 K₂O3.0 3.00 3.00 Nd₂O₃ 5.0 5.0 5.00 α_(25-300° C.)(10⁻⁶/° C.) 8.47 6.256.23 Tg (° C.) 675 599 597 Td (° C.) 712 662 646

[0099] Example 47 is a modification of example 5 (Table I) in which K₂Oand Nd₂O₃ were substituted for part of BaO and CaO. Example 47 still hashigh expansion. Examples 48 and 49 illustrate how to decrease theexpansion to the desired range (˜6×10⁻⁶/° C.) and simultaneouslydecrease the softening properties (as expressed by the decrease in Tg orTd). Nd₂O₃ is used as an example of rare earth oxides. Other rare earthoxides can be used as such, or their mixtures.

[0100] Compositional range of glasses of table XI is (in mole %): SiO₂40-60 B₂O₃  1-20 BaO  1-15 SrO 1-6 CaO  1-15 CuO 0.5-3   ZnO 0.5-20 M₂O₃ 0.25-7   M′₂O 0.25-4  

[0101] Table XII presents the electrical properties of resistorcompositions formulated with example 48 glass, example 1 conductive andtwo TCR modifiers Nb₂O₅ and TiO₂. Examples 50 to 53 were prepared on themuller and example 54 is a roll milled composition derived from examples50 and 51. TiO₂ is a very efficient TCR modifier as examples 52 and 53show; it raises the resistance and lowers the TCR. These examples alsoillustrate how to raise the resistance and maintain positive TCR(example 54) and how to lower the TCR at a given conducting phaseconcentration (examples 52 and 53). Examples 50 and 51 show that Nb₂O₅is not as efficient as TiO₂ in lowering the TCR in these compositions.TABLE XII Compositions in wt % and electrical properties Example No. 5051 52 53 54 Ex. 1 conductive 20.0 15.0 20.0 20.0 13.75 Ex. 48 glass 39.044.0 39.0 38.5 45.25 ZrSiO₄ 10.5 10.5 10.5 10.5 10.50 Nb₂O₂ 0.5 0.5 — —0.50 TiO₂ — — 0.5 1.0 — Organic vehicle 30.0 30.0 30.0 30.0 30.0 Rav(kΩ/) 1.61 14.27 8.52 42.7 470.0 HTCR(ppm/° C.) 1223.8 1501.2 403.7−370.1 428.2 σ_(HTCR)(ppm/° C.) ±89.4 ±73.0 ±59.7 ±157.1 ±246.2CTCR(ppm/° C.) 1384.2 1893.8 486.3 −563.8 524.4 σ_(CTCR)(ppm/° C.)±168.5 ±102.9 ±76.2 ±238.8 ±288.5

[0102] TABLE XIII Compositions in wt % and electrical properties ExampleNo. 55 56 57 Ex.1 conductive 12.5 12.5 12.5 Ex.48 glass 46.5 44.0 45.5ZrSiO₄ 10.5 13.0 12.0 Nb₂O₅ 0.5 0.5 — Organics 30.0 30.0 30.0 R (M/) * ***

[0103] Examples 55 to 57 show that at 12.5 wt % conductive, theresistance is very high when Nb₂O₅ is present (examples 55 & 56) and itis in the range of 100 to 200 M / when Nb₂O₅ is not included (example57). Resistor compositions in the range of 1 M / and higher can beformulated with mixtures (blends) consisting of example 54 andcomposition of Table XIII.

[0104] While specific embodiments of the invention have been describedfor the purpose of illustration, it will be understood that theinvention may be carried into practice by skilled persons with manymodifications, variations and adaptations, without departing from itsspirit or exceeding the scope of the claims.

1. Film compositions that comprise, as a conductive phase,pyrochlore-related compounds of the general formula M_(2-x) Cu_(x) Ru₂O_(6+δ), wherein M is a rare earth metal selected from the rare earthmetals of atomic number 60-71 inclusive.
 2. Compositions according toclaim 1, wherein X=0.2-0.4 and δ=0-1.
 3. Compositions according to claim1, comprising a dielectric phase.
 4. Compositions according to claim 3,wherein the dielectric phase consists of or comprises, as a maincomponent, a glass phase.
 5. Compositions according to claim 4, whereinthe glass phase comprises by mole % 40-60% SiO₂, 1-20% B₂O₃, 1-15% BaO,1-6% SrO, 1-15% CaO, 0.5-3% CuO, 0.5-20% ZnO, 0.25-7% M₂O₃, 0.25-4%M′₂O, wherein M′ is Li, Na, K or mixture thereof, and M is a rare earthelement of atomic number 57 to 71 inclusive, or mixture thereof; and0-3% of a metal fluoride in which the metal is selected from the groupconsisting of alkali and alkaline earth metals.
 6. Compositionsaccording to claim 4, wherein the glass phase comprises by mole % 40 to65% SiO₂, 10 to 20% Bi₂O₃, 0.1 to 3% Al₂O₃, and glass modifiers in totalamount of 15 to 25%, wherein said glass modifiers comprise 1 to 23% ZnO,0.1 to 5% CuO, 0.1 to 5% CaO and 0.1 to 2% MgO.
 7. Compositionsaccording to claim 4, wherein the glass phase comprises a blend of twoglasses.
 8. Compositions according to claim 7, wherein a) a first glasscomprises by mole % 40-65% SiO₂, 1-15% B₂O₃, 12-27% BaO, 5-10% SrO,5-15% CaO, 0-5% MgO, 0-5% Al₂O₃, 0-12% alkali metal oxides and 0-3% of ametal fluoride in which the metal is selected from the group consistingof alkali and alkaline earth metals; and b) a second glass comprises bymole % glass forming compounds in a total amount of 75 to 85% wherein,said glass forming compounds comprise 40 to 65% SiO₂, 10 to 20% Bi₂O₃,0.1 to 3% Al₂O₃, and glass modifiers in total amount of 15 to 25%,wherein said glass modifiers comprise 1 to 23% ZnO, 0.1 to 5% CuO, 0.1to 5% CaO and 0.1 to 2% MgO.
 9. Compositions according to claim 3 or 4,wherein the dielectric phase is selected from Al₂O₃, SiO₂, ZrSiO₄, ZrO₂,aluminosilicates and mixtures thereof.
 10. Compositions according toclaim 1, further comprising an organic vehicle.
 11. Compositionsaccording to claim 10, wherein the organic vehicle is a solution ofresin in a solvent or mixture of solvents.
 12. Compositions according toclaim 1, further comprising a filler.
 13. Compositions according toclaim 12, wherein the filler is chosen from the group consisting ofAl₂O₃, SiO₂, ZrSiO₄, ZrO₂ and aluminosilicates.
 14. Compositionsaccording to claim 1, comprising a) a dispersion of finely dividedparticles of the pyrochlore—related compound corresponding to theformula M_(2-x) Cu_(x) Ru₂ O_(6+δ), wherein M is a rare earth metalselected from the rare earth metals of atomic number 60-71 inclusive,X=0.2-0.4 , δ=0-1; b) glasses according to claims 5, 6, 7, 8, andmixtures thereof; and c) dielectrics selected from the group consistingof SiO₂, ZrSiO₄ and Al₂O₃.
 15. Compositions according to claim 14,wherein the rare earth metal is Neodymium.
 16. A composition accordingclaim 4, wherein the glass phase comprises glasses chosen from the groupconsisting of Cd-free and Pb-free bismuthate glasses, alkaline earthborosilicate glasses, and mixture thereof.
 17. A composition accordingto claim 4, wherein the glass phase is chosen from the group consistingof lead-containing silicate glasses, lead-containing borosilicateglasses and mixtures thereof.
 18. Method of preparing pyrochlore-relatedcompounds as defined in claim 1, which comprises firing an admixture offinely divided particles of CuO, RuO₂ and a metal oxide selected fromthe rare earth metal oxides of atomic number 60-71 inclusive, at atemperature of at least 800° C., in a non-reducing atmosphere. 19.Method according to claim 18, for preparing compounds having the formulaNd_(2-x) Cu_(x) Ru₂ O_(6+δ), which comprises firing in air an admixtureof finely divided particles of Nd₂O₃, CuO and RuO₂ at a temperature of1000-1200° C.
 20. Method of making film compositions according to claim1, comprising preparing a powdered mixture of a) 5-90% by weight of anoxide of the formula Cu_(x) M_(2-x) Ru₂ O_(6+δ), wherein M is a rareearth metal selected from the rare earth metals of atomic number 60-71inclusive, x is a number in the range of 0.25 to 0.4, and δ is a numberin the range of 0 to 1; and b) 95-10% by weight of dielectric materials.21. Method according to claim 20, further comprising dispersing thepowdered mixture in a liquid organic vehicle.
 22. Method according toclaim 20, wherein the oxide is chosen from the group consisting ofNd_(1.70) Cu_(0.30) Ru₂ O_(6+δ), Nd_(1.75) Cu_(0.25) Ru₂ O_(6+δ), andtheir mixtures wherein δ is a number in the range of 1 to
 0. 23. Methodaccording to claim 22, wherein the dielectric materials are chosen fromthe group consisting of glasses, oxides selected from ZrSiO₄, Al₂O₃,SiO₂, and mixture thereof.
 24. Film compositions, substantially asdescribed and illustrated.
 25. Method of preparing pyrochlore-relatedcompounds as defined in claim 1, substantially as described andillustrated.
 26. Method of making film compositions according to claim1, substantially as described and illustrated.